Darwin Glacier, Kings Canyon National Park. This image illustrates
glacier change in the Sierra Nevada. The image toggles between a
photograph taken on August 14, 1908 by G.K. Gilbert and a
photograph taken on August 2, 2003 by Hassan Basagic.

Glaciers of the Sierra Nevada

This page highlights my research on glacier change in the Sierra Nevada.
A publication and my thesis entitled "Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California" are available:
Thesis (2008)Publication (2011)
Numerous small alpine glaciers occupy the high elevation regions of the central
and southern Sierra Nevada, California. These glaciers change size in
response to variations in climate and are therefore important
indicators of climate change. While knowledge of glacier shrinkage in
the Sierra Nevada is common, there was little quantitative information
on the magnitude or rate of reduction. The purpose of my thesis was to define the number and spatial extent of the Sierra Nevada glacier
population, quantify the magnitude and rate of change in glacier extent for a small
subset of glacier, and compare the rates of change against climate variations.

Where do glaciers occur in the
Sierra Nevada?

Glaciers
are found high in the Sierra Nevada, generally above 10,000 feet in
elevation, on the north sides of steep mountains from Yosemite
National Park in the north to Sequoia National Park in the
south. Sierra Nevada glaciers are typically located in mountain
cirques, which are small bowl-like
depressions on the sides of mountains which were created by previous
glaciers.

The
number of glaciers in the Sierra Nevada depends on the definition.
The definition of a glacier is a body of perennial ice or snow that moves. Movement of ice
can be observed as cracks in the ice known as crevasses. Because Sierra Nevada
glaciers are small and remote previous glacier inventories
have placed the number between 50 and 500 glaciers. My
survey, based on USGS topographic maps (1:24,000 scale),
counted over 1700 glaciers and snow and ice patches. Many snow and ice bodies which
do meet the definition of a glacier. I estimated the number of "true glaciers" at 118
glaciers in the Sierra Nevada based on theoretical considerations.

The central and
southern Sierra Nevada with glaciers highlighted in red to show modern
extent (MODIS image)

How have glaciers changed over
the past century?

Sierra
Nevada glaciers have become smaller over the past century. This is
evident from early photographs which reveal these glaciers occupying
their moraines around 1900. Today, the glaciers have receded up the
mountains and appear deflated. I quantified the surface area change by
selecting
fourteen glaciers throughout the Sierra Nevada and measured
the change using historical photographs, geologic evidence,
and field mapping. I determined the glaciers lost and average
of 55 percent of their surface area by 2004. The decrease in surface
area of individual glaciers ranged between 31 and 78 percent.

I selected
a subset of seven glaciers to determine the rate of change
over the past century. The results indicated that glaciers rapid
retreated occurred over the first half of the twentieth century
beginning in the 1920s in response to warm/dry conditions and continued
through
the mid-1970s. Recession ceased during the early 1980s, when some
glaciers
advanced. Since the 1980s each of the seven study glaciers resumed
retreat.

Glacier Repeat
Photography

Comparisons
of the repeat photographs reveal that all ten glaciers surveyed in 2003
and 2004 have experienced a reduction in ice volume and surface extent
over the past century. Repeat photography is a valuable tool in
determining change through time, especially when combined with aerial
photos and field measurements. Please
contact me if you are interested in using these photographs.

Darwin Glacier

August 14, 1908
G.K. Gilbert

August 14, 2004
H. Basagic

Lyell Glacier

August 7, 1903 G.K.
Gilbert

August 14, 2003
H. Basagic

Dana Glacier

August, 1883 I.C.
Russell

September 8, 2004
H.
Basagic

Sierra
Nevada Glacier Photographs

Here
are some examples of glaciers in the Sierra Nevada from the Glaciers of the American West Photo Archive: